Organic light emitting display device

ABSTRACT

An organic light emitting display device includes an active layer of a transistor disposed on a substrate, a gate electrode disposed on the active layer and on a first insulation layer, a second insulation layer which is disposed on the gate electrode and exposes a source area and a drain area of the active layer, a drain electrode which is disposed on the second insulation layer and is connected to an exposed area of the drain area, a third insulation layer on the drain electrode, and a cathode electrode on the third insulation layer, where the cathode electrode penetrates the first insulation layer, the second insulation layer and the third insulation layer, and the cathode electrode is connected to an exposed area of the source area.

This application claims priority to Korean Patent Application No.10-2013-0061261, filed on May 29, 2013, and all the benefits accruingtherefrom under 35 U.S.C. §119, the disclosure of which is incorporatedherein in its entirety by reference.

BACKGROUND

1. Field

The invention relates to an organic light emitting display device, andmore particularly, to an organic light emitting display device which mayimprove an aperture ratio.

2. Description of the Related Art

An organic light emitting display device has superior characteristics interms of a viewing angle, contrast, response speed and consumptionpower, for example, and thus an application range is being extended frompersonal portable devices such as MP3 players and mobile phones to atelevision (“TV”).

Such an organic light emitting display device generally includes aplurality of pixels including one or more transistors and capacitors,and operation of the pixels may be divided into an initializationperiod, a compensation/data transfer period, and a scan/emission period.

Furthermore, in the initialization period, an initialization voltage isapplied to an initialization transistor included in each pixel, andgenerally, the initialization voltage is supplied by an initializationvoltage line which is separately formed in the pixel. Furthermore, a viahole is defined in each pixel for electrically connecting theinitialization voltage line with the initialization transistor.

SUMMARY

The invention provides an organic light emitting display device whichmay improve an aperture ratio.

According to an exemplary embodiment of the invention, there is providedan organic light emitting display device including an active layer of atransistor disposed on a substrate, a gate electrode disposed on theactive layer and on a first insulation layer, a second insulation layerthat is disposed on the gate electrode and exposes a source area and adrain area of the active layer, a drain electrode that is disposed onthe second insulation layer and is connected to an exposed area of thedrain area, a third insulation layer on the drain electrode, and acathode electrode on the third insulation layer, where the cathodeelectrode penetrates the first insulation layer, the second insulationlayer and the third insulation layer, and the cathode electrode isconnected to an exposed area of the source area.

The organic light emitting display device may further include a sourceelectrode between the source area and the cathode electrode.

The transistor may be an initialization transistor.

The cathode electrode may apply an initialization voltage to theinitialization transistor.

The initialization voltage may be a voltage applied to the cathodeelectrode.

The organic light emitting display device may further include an organiclight emitting device including an anode electrode on the firstinsulation layer, an organic light emitting layer on the anodeelectrode, and the cathode electrode on the organic light emittinglayer.

The organic light emitting display device may further include acapacitor including a lower electrode under the first insulation layerand an upper electrode on the first insulation layer, where the firstinsulation layer is a dielectric layer.

The organic light emitting display device may further include a bufferlayer on the substrate.

The organic light emitting display device may further include a sealingmember on the cathode electrode.

According to another aspect of the invention, there is provided anorganic light emitting display device including an organic lightemitting device (“OLED”) including an anode electrode, a cathodeelectrode, and an organic light emitting layer disposed between theanode electrode and the cathode electrode, and a pixel circuit thatsupplies electric current to the OLED, where the pixel circuit includesan initialization transistor, where a source area of the initializationtransistor is connected to the cathode electrode, and the cathodeelectrode applies an initialization voltage to the initializationtransistor.

A first power voltage may be applied to the anode electrode, and asecond power voltage may be applied to the cathode electrode, where thesecond power voltage is the initialization voltage and is applied to theinitialization transistor.

The pixel circuit may further include a driving transistor, where adrain area of the initialization transistor is connected to a gateelectrode of the driving transistor.

A second power voltage may be applied to the gate electrode of thedriving transistor as a gate signal.

The initialization transistor may include an active layer disposed on asubstrate, a gate electrode disposed on a first insulation layer that isdisposed on an active layer, a drain electrode connected to a drain areaof the active layer exposed by a contact hole of a second insulationlayer that is disposed on the gate electrode, and a third insulationlayer on the drain electrode, where the cathode electrode penetrates thefirst insulation layer, the second insulation layer and the thirdinsulation layer.

The organic light emitting display device may further include a sourceelectrode between the source area and the cathode.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the invention will becomemore apparent by describing in detail exemplary embodiments thereof withreference to the attached drawings in which:

FIG. 1 is a block diagram schematically illustrating an organic lightemitting display device according to an exemplary embodiment of theinvention;

FIG. 2 is a circuit diagram of a pixel of the organic light emittingdisplay device of FIG. 1;

FIG. 3 is a timing diagram illustrating an operation of the pixel ofFIG. 2;

FIG. 4 is a diagram schematically illustrating some components of theorganic light emitting display device of FIG. 1; and

FIG. 5 is a diagram schematically illustrating a modified example of theorganic light emitting display device of FIG. 4.

DETAILED DESCRIPTION

An initialization voltage line and a via hole respectively occupy acertain area. Therefore, when an initialization voltage is supplied bythe initialization voltage line, a pixel opening is reduced according tothe area where the initialization voltage line and the via hole aredisposed.

The invention will now be described more fully with reference to theaccompanying drawings, in which exemplary embodiments of the inventionare shown. The invention may, however, be embodied in many differentforms and should not be construed as being limited to the embodimentsset forth herein; rather, these embodiments are provided so that thisdisclosure will be thorough and complete, and will fully convey theconcept of the invention to those skilled in the art. In the drawings,the thicknesses of layers and regions are exaggerated for clarity. Likereference numerals in the drawings denote like elements, and thus theirdescription will be omitted.

The invention now will be described more fully hereinafter withreference to the accompanying drawings, in which various embodiments areshown. This invention may, however, be embodied in many different forms,and should not be construed as limited to the embodiments set forthherein. Rather, these embodiments are provided so that this disclosurewill be thorough and complete, and will fully convey the scope of theinvention to those skilled in the art. Like reference numerals refer tolike elements throughout.

It will be understood that when an element is referred to as being “on”another element, it can be directly on the other element or interveningelements may be present therebetween. In contrast, when an element isreferred to as being “directly on” another element, there are nointervening elements present.

It will be understood that, although the terms “first,” “second,”“third” etc. may be used herein to describe various elements,components, regions, layers and/or sections, these elements, components,regions, layers and/or sections should not be limited by these terms.These terms are only used to distinguish one element, component, region,layer or section from another element, component, region, layer orsection. Thus, “a first element,” “component,” “region,” “layer” or“section” discussed below could be termed a second element, component,region, layer or section without departing from the teachings herein.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting. As used herein, thesingular forms “a,” “an,” and “the” are intended to include the pluralforms, including “at least one,” unless the content clearly indicatesotherwise. “Or” means “and/or.” As used herein, the term “and/or”includes any and all combinations of one or more of the associatedlisted items. It will be further understood that the terms “comprises”and/or “comprising,” or “includes” and/or “including” when used in thisspecification, specify the presence of stated features, regions,integers, steps, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,regions, integers, steps, operations, elements, components, and/orgroups thereof.

Furthermore, relative terms, such as “lower” or “bottom” and “upper” or“top,” may be used herein to describe one element's relationship toanother elements as illustrated in the Figures. It will be understoodthat relative terms are intended to encompass different orientations ofthe device in addition to the orientation depicted in the Figures. Forexample, if the device in one of the figures is turned over, elementsdescribed as being on the “lower” side of other elements would then beoriented on “upper” sides of the other elements. The exemplary term“lower,” can therefore, encompasses both an orientation of “lower” and“upper,” depending on the particular orientation of the figure.Similarly, if the device in one of the figures is turned over, elementsdescribed as “below” or “beneath” other elements would then be oriented“above” the other elements. The exemplary terms “below” or “beneath”can, therefore, encompass both an orientation of above and below.

In the case where a position relationship between two items aredescribed with the terms “on ˜,” “under ˜,” or the like, one or moreitems may be interposed therebetween unless a description is given usingthe term “directly”.

FIG. 1 is a block diagram schematically illustrating an organic lightemitting display device 1 according to an exemplary embodiment of theinvention.

Referring to FIG. 1, the organic light emitting display device 1 mayinclude a display panel 10 including a plurality of pixels P, a scandriver 20, a data driver 30 and a controller 40.

The scan driver 20, the data driver 30, and the controller 40 may berespectively disposed in a separate semiconductor chip, or may beintegrated in one semiconductor chip. Furthermore, the scan driver 20and the display panel 10 may be disposed on the same substrate.

A plurality of scan lines SL is horizontally disposed on the displaypanel 10, and a plurality of data lines DL, which perpendicularlycrosses the scan lines SL, is vertically disposed on the display panel10. A plurality of pixels P is disposed in a matrix form. In oneexemplary embodiment, the pixels P may be in areas between intersectionsof the plurality of scan lines SL and the plurality of data lines DL,but the invention is not limited thereto.

Furthermore, though not illustrated in FIG. 1, various types of linessuch as a plurality of light emitting control lines that supplies lightemitting control signals, a driving voltage line that supplies a powervoltage, for example, may be additionally disposed on the display panel10.

However, an initialization voltage line for supplying an initializationvoltage Vint is not separately provided, and a second power voltageELVSS may be supplied as the initialization voltage Vint by a cathodeelectrode (120 of FIG. 4). Hence, a formation of the initializationvoltage line and a via hole for electrically connecting theinitialization voltage line with an initialization transistor (TC3 ofFIG. 2) may be omitted, and, as such, a space for widely designing apixel opening may be provided, thereby improving an aperture ratio ofthe organic light emitting display device 1, which will be described indetail later with reference to FIGS. 2 to 4.

The scan driver 20 may generate scan signals and sequentially providethe generated scan signals to the display panel 10 through the pluralityof scan lines SL.

The data driver 30 may sequentially provide data signals to the displaypanel 10 through the plurality of data lines DL. The data driver 30converts input image data DATA having a grayscale input from thecontroller 40 into data signals in a form of a voltage or a currentsignal.

The controller 40 generates a scan control signal (“SCS”) and a datacontrol signal (“DCS”), and respectively transmits the SCS and the DCSto the scan driver 20 and the data driver 30. As such, the scan driver20 sequentially applies scan signals for scan lines, and the data driver30 applies data signals to respective pixels P. Furthermore, a firstpower voltage ELVDD, the second power voltage ELVSS, a light emittingcontrol signal EM, for example, may be applied to respective pixels Punder control of the controller 40.

FIG. 2 is a circuit diagram of a pixel P according to an exemplaryembodiment of the invention, and FIG. 3 is a timing diagram illustratingan operation of the pixel P of FIG. 2.

Referring to FIG. 2, the pixel P includes an organic light emittingdevice (“OLED”) and a pixel circuit C for supplying electric current tothe OLED.

An anode electrode (114 of FIG. 4) of the OLED is connected to the pixelcircuit C, and the cathode electrode (120 of FIG. 4) is connected to asecond power source that supplies the second power voltage ELVSS. TheOLED emits light at a predetermined luminance in response to the currentsupplied from the pixel circuit C.

In an exemplary embodiment, the pixel circuit C may include eighttransistors TC1 to TC8 and two capacitors C1 and C2, for example.

Scan signals S may be applied to a gate electrode of the firsttransistor TC1 from scan lines, a first electrode of the firsttransistor TC1 may be connected to the data line and data signals D maybe applied to the first electrode, and a second electrode of the firsttransistor TC1 may be connected to the first node N1.

A first control signal GW may be applied to a gate electrode of a secondtransistor TC2, a first electrode of the second transistor TC2 may beconnected to the first node N1, and a second electrode of the secondtransistor TC2 may be connected to a second node N2.

A second control signal GI may be applied to a gate electrode of thethird transistor TC3, a first electrode of the third transistor TC3 maybe connected to the cathode electrode of the OLED, and the second powervoltage ELVSS may be applied to the first electrode of the thirdtransistor TC3 as the initialization voltage Vint, and a secondelectrode of the third transistor TC3 may be connected to the third nodeN3. That is, the third transistor TC3 operates as an initializationtransistor.

The first control signal GW may be applied to a gate electrode of afourth transistor TC4, a first electrode of the fourth transistor TC4may be connected to the third node N3, and a second electrode of thefourth transistor TC4 may be connected to a fourth node N4.

The second control signal GI may be applied to the gate electrode of afifth transistor TC5, a first electrode of the fifth transistor TC5 maybe connected to a first power source that supplies the first powervoltage ELVDD and the first power voltage ELVDD may be applied to thefirst electrode of the fifth transistor TC5, and a second electrode ofthe fifth transistor TC5 may be connected to the second node N2.

A gate electrode of a sixth transistor TC6 may be connected to the thirdnode N3, a first electrode of the sixth transistor TC6 may be connectedto the second node N2 and a second electrode of the sixth transistor TC6may be connected to the fourth node N4. The sixth transistor TC6 mayoperate as a driving transistor, and the second power voltage ELVSS maybe applied to the gate electrode of the sixth transistor TC6 as a gatesignal.

A third control signal GE may be applied to a gate electrode of aseventh transistor TC7, a first electrode of the seventh transistor TC7may be connected to fourth node N4, and a second electrode of theseventh transistor TC7 may be connected to the anode electrode (114 ofFIG. 4) of the OLED.

The third control signal GE may be applied to a gate electrode of aeighth transistor TC8, a first electrode of the eighth transistor TC8may be connected to the first power source that supplies the first powervoltage ELVDD and the first power voltage ELVDD may be applied to thefirst electrode of the eighth transistor TC8, and a second electrode ofthe eighth transistor TC8 may be connected to the second node N2.

A first capacitor C1 may be connected between the first node N1 and athird power source that supplies a third power voltage Vhold. When thefirst transistor TC1 is turned on, the first capacitor C1 charges avoltage corresponding to the data signal D supplied from the data line.The third power source may be a fixed power source (e.g., DC powersource) having a predetermined voltage. In an exemplary embodiment, thethird power source may be the same as the first power source thatsupplies the first power voltage ELVDD, for example, but the inventionis not limited thereto. A second capacitor C2 may be connected betweenthe third node N3 and the first power source.

Referring to FIG. 3, each pixel P operates in a simultaneouslight-emitting scheme, and the operation may be divided into aninitialization period (Int), a compensation/data transfer period(Vth/Dtrans), and a scan/emission period (Scan/Emission). In thescan/emission period (Scan/Emission), scan signals are sequentiallyinput to respective scan lines, and in response thereto, data signalsare sequentially input to respective pixels P. Initialization andthreshold voltage compensation of a driving transistor included inrespective pixels P, data transfer, and light-emitting operation ofrespective pixels P may be simultaneously implemented for respectiveframes.

In the initialization period (Int), the first power voltage ELVDD isapplied at a high level, and the second power voltage ELVSS and thesecond control signal GI are applied at a low level. As such, the thirdtransistor TC3 and the fifth transistor TC5 are turned on, and the firstpower voltage ELVDD is applied to the second node N2, and theinitialization voltage Vint is applied to the third node N3.

Furthermore, according to the exemplary embodiment of the invention, theinitialization voltage line for supplying the initialization voltageVint may not be separately provided, the cathode electrode (120 of FIG.4) may be connected to the third transistor TC3 and the second powervoltage ELVSS may be applied to the third node N3 as the initializationvoltage Vint.

Both the initialization voltage Vint and the second power voltage ELVSSmay be set as a ground voltage, and the initialization voltage Vint maybe substituted by the second power voltage ELVSS. Hence, aninitialization voltage line may be removed and the pixel opening may bedesigned to be as wide as an area of the removed initialization voltageline, and thus an aperture ratio of the organic light emitting displaydevice 1 may be effectively improved.

In the compensation/data transfer period Vth/Dtrans, the first powervoltage ELVDD, the second power voltage ELVSS and the first controlsignal GW are applied at a low level. As such, the second transistor TC2is turned on, and the data signals D written in the pixels in a scanperiod of N−1 frames which have been stored in the first capacitor C1are transferred to the second node N2. Furthermore, the fourthtransistor TC4 is turned on and the sixth transistor TC6 isdiode-connected, electric current flows through the diode-connectedsixth transistor TC6, and a threshold voltage of the sixth transistorTC6 is compensated and the voltage difference between the first powervoltage ELVDD and the second node N2 is stored in the second capacitorC2.

In the scan/emission period (Scan/Emission), the scan period and theemission period are simultaneously performed. In the scan/emissionperiod (Scan/Emission), the first power voltage ELVDD is applied at ahigh level, and the second power voltage ELVSS and the third controlsignal GE are applied at a low level. Furthermore, the scan signals (S1to Sn+1) of low level are sequentially input to respective scan lines,and the first transistor TC1 is turned on and data signals of N framesare sequentially input to pixels P connected to respective scan lines.

Furthermore, the second transistor TC2 is turned off to block the firstnode N1 and the second node N2. Also, the seventh and eighth transistorsTC7 and TC8 are turned on and thus a current path from the first powervoltage ELVDD to the cathode of the OLED is formed via the turned-onfifth transistor TC5, the turned-on sixth transistor TC6 and theturned-on seventh transistor TC7, and the OLED emits light to abrightness corresponding to a data signal written in the emission pixelP in the scan period of a (N−1)th frame stored in the second capacitorC2. At this time, all pixels P sequentially emit light. That is, in thescan/emission period (Scan/Emission), data signals of the Nth frame aresequentially input according to scan signals and, at the same time, eachemission pixel P emits light in correspondence with data signals of the(N−1)th frame. Furthermore, the emission period (Emission) may bepartially overlapped with the scan period, and may be performed for ashorter period of time than the scan period (Scan).

Here, a width of the sequentially applied scan signals S1 to Sn+1 may beapplied as two horizontal hours (2H), and widths of the adjacent scansignals, for example, a width of the (n−1)th scan signal (Sn−1) and awidth of the nth scan signal (Sn) may be applied to be overlapped byless than one horizontal hour (1H). This is to overcome an insufficientcharge situation according to an RC delay of the signal lines due to alarge size of a display area of the OLED device.

FIG. 4 is a diagram schematically illustrating components of the organiclight emitting display device 1, and FIG. 5 is a diagram schematicallyillustrating a modified example P′ of pixels P of the organic lightemitting display device of FIG. 4.

As described above with regard to FIG. 2, each pixel P includes eighttransistors TC1 to TC8, two capacitors C1 and C2, scan lines SL, datalines DL, for example, but only the OLED, the third transistor TC3, andthe first capacitor C1 are illustrated in FIGS. 4 and 5, and thecomponents thereof will be described in detail.

First, a substrate 100 may include transparent glass including SiO₂.However, in an exemplary embodiment, the substrate 100 may includetransparent plastic.

A buffer layer 111 may be disposed on the substrate 100. The bufferlayer 111 provides a substantially flat plane on an upper part of thesubstrate 100 and effectively prevents infiltration of moisture andalien substances.

The third transistor TC3 may include an active layer 212, a gateelectrode 214, and a drain electrode 216.

Specifically, the active layer 212 of the third transistor TC3 isdisposed on the buffer layer 111. The active layer 212 may include aninorganic semiconductor material such as amorphous silicon andpolysilicon, for example. Furthermore, the active layer 212 may includean organic semiconductor material, an oxide semiconductor material orother various materials. The active layer 212 includes a source area 212b and a drain area 212 a provided by doping of impurities, and a channelarea 212 c between the source area 212 b and the drain area 212 a.

A gate electrode 214 is disposed on the active layer 212 at a positioncorresponding to the channel area 212 c of the active layer 212 while afirst insulation layer 113 is disposed between the gate electrode 214and the active layer 212. The second control signal (GI FIG. 2) isapplied to the gate electrode 214.

A second insulation layer 115 that is an inter-metal dielectric layer isdisposed on the gate electrode 214. A contact hole is defined in thesecond insulation layer 115 and exposes the drain area 212 a and thesource area 212 b of the active layer 212.

The drain electrode 216 connected to the drain area 212 a of the activelayer 212 exposed by the contact hole is disposed on the secondinsulation layer 115, and a third insulation layer 118 is disposed onthe drain electrode 216. The third insulation layer 118 may be providedas an organic insulation layer.

A via hole is defined in the first insulation layer 113, the secondinsulation layer 115 and the third insulation layer 118, and the cathodeelectrode 120 is connected to the source area 212 b through the viahole.

That is, the cathode electrode 120 may penetrate the first insulationlayer 113, the second insulation layer 115, and the third insulationlayer 118 to directly contact the source area 212 b of the active layer212. As described above with regard to FIG. 2, the cathode electrode 120is connected to the second power source that supplies the second powervoltage ELVSS, and thus the second power voltage ELVSS may be applied tothe third transistor TC3, which is the initialization transistor, as theinitialization voltage Vint.

However, the invention is not limited thereto, and the source electrode218 connected to the source area 212 b may be further included in thethird transistor TC3 as illustrated in FIG. 5. Here, the cathodeelectrode 120 is electrically connected to the source electrode 218through the via hole.

Likewise, when the initialization voltage Vint is applied by the cathodeelectrode 120, the initialization voltage line for supplying theinitialization voltage Vint may not be separately configured. That is,the pixel opening may be designed to be as wide as the area where theinitialization voltage line is to be arranged. Generally, theinitialization voltage line is longitudinally disposed along one sidedirection of the pixel P and a width of the initialization voltage lineis about 20 micrometers (μm). Hence, when the initialization voltageline is removed, the aperture ratio of the organic light emittingdisplay device 1 may be increased by about 7 to 8 percent (%).

The OLED may include the anode electrode 114, an organic light emittinglayer 119, and the cathode electrode 120.

Specifically, the anode electrode 114 may be disposed on the bufferlayer 111 and the first insulation layer 113. The anode electrode 114may include transparent conductive materials which are the same as thegate electrode 214. The transparent conductive materials may include atleast one selected from indium tin oxide (“ITO”), indium zinc oxide(“IZO”), indium gallium oxide (“IGO”), aluminum zinc oxide (“AZO”). Theanode electrode 114 is connected to the pixel circuit (C of FIG. 2).

The organic light emitting layer 119 may be disposed on the anodeelectrode 114, and light emitted from the organic light emitting layer119 may be emitted toward the substrate 100 through the anode electrode114.

The organic light emitting layer 119 may include low molecular organicmatter or high molecular organic matter. When the organic light emittinglayer 119 includes low molecular organic matter, a hole transport layer(“HTL”), a hole injection layer (“HIL”), an electron transport layer(“ETL”), an electron injection layer (“EIL”), for example, may bestacked. In addition, various other layers may also be stacked asnecessary. Here, exemplary embodiments of organic matter include copperphthalocyanine (“CuPc”), N′-Di(naphthalene-1-yl)-N,N′-diphenyl-benzidine (“NPB”), tris-8-hydroxyquinoline aluminum (Alq3),for example.

Furthermore, when the organic light emitting layer 119 includes highmolecular organic matter, the HTL may be included in addition to theorganic light emitting layer 119. The HTL may usepoly-(3,4)-ethylene-dihydroxy thiophene (“PEDOT”), polyaniline (“PANI”),etc. At this time, exemplary embodiments of usable organic matterinclude high molecular organic matter such as Poly-Phenylenevinylene(“PPV”) and Polyfluorene based matter.

The cathode electrode 120 is disposed on the organic light emittinglayer 119 as a common electrode, and the cathode electrode 120 isconnected to the second power source, which supplies the second powervoltage ELVSS.

The cathode electrode 120 may include a reflective electrode. Here, thecathode electrode 120 may contain at least one selected from Al, Mg, Li,Ca, LiF/Ca, LiF/AI, and combination thereof.

The cathode electrode 120 is provided as a reflective electrode, andthus light emitted from the organic light emitting layer 119 isreflected in the cathode electrode 120 and penetrates the anodeelectrode 114 including transparent conductive materials so as to beemitted toward the substrate 100.

The first capacitor C1 may include a lower electrode 312 and an upperelectrode 314 that are respectively disposed on and under the firstinsulation layer 113 where the first insulation layer 113 is thedielectric layer.

Specifically, the lower electrode 312 of the first capacitor C1 includesthe same materials as those of the active layer 212, and is disposed onthe substrate 100 and the buffer layer 111. The upper electrode 314 ofthe first capacitor C1 includes the same materials as those of the anodeelectrode 114 and is disposed on the first insulation layer 113.

Furthermore, though not illustrated in FIGS. 4 and 5, a sealing member(not shown) may be disposed on an upper part of the cathode electrode120. The sealing member (not shown) is disposed to protect the organiclight emitting layer 119 from external moisture or oxygen, for example,and may include glass or plastic or may have a structure in which aplurality of organic layers and inorganic layers are stacked.

According to an exemplary embodiment of the invention, a space forwidely designing a pixel opening may be provided by removing aninitialization voltage line, thereby improving an aperture ratio of anorganic light emitting display device.

While the invention has been particularly shown and described withreference to exemplary embodiments thereof, it will be understood bythose of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the invention as defined by the following claims.

What is claimed is:
 1. An organic light emitting display devicecomprising: an active layer of a transistor disposed on a substrate; agate electrode disposed on the active layer and on a first insulationlayer; a second insulation layer which is disposed on the gate electrodeand exposes a source area and a drain area of the active layer; a drainelectrode which is disposed on the second insulation layer and isconnected to an exposed area of the drain area; a third insulation layeron the drain electrode; and a cathode electrode on the third insulationlayer, wherein the cathode electrode penetrates the first insulationlayer, the second insulation layer and the third insulation layer, andthe cathode electrode is connected to an exposed area of the sourcearea.
 2. The organic light emitting display device of claim 1, furthercomprising: a source electrode between the source area and the cathodeelectrode.
 3. The organic light emitting display device of claim 1,further comprising: an organic light emitting device including an anodeelectrode on the first insulation layer; an organic light emitting layeron the anode electrode; and the cathode electrode on the organic lightemitting layer.
 4. The organic light emitting display device of claim 1,further comprising: a capacitor including a lower electrode under thefirst insulation layer and an upper electrode on the first insulationlayer, wherein the first insulation layer is a dielectric layer.
 5. Theorganic light emitting display device of claim 1, further comprising: abuffer layer on the substrate.
 6. The organic light emitting displaydevice of claim 1, further comprising: a sealing member on the cathodeelectrode.
 7. The organic light emitting display device of claim 1,wherein the transistor is an initialization transistor.
 8. The organiclight emitting display device of claim 7, wherein the cathode electrodeapplies an initialization voltage to the initialization transistor. 9.The organic light emitting display device of claim 8, wherein theinitialization voltage is a voltage applied to the cathode electrode.10. An organic light emitting display device comprising: an organiclight emitting device including an anode electrode, a cathode electrode,and an organic light emitting layer disposed between the anode electrodeand the cathode electrode; and a pixel circuit which supplies electriccurrent to the organic light emitting device and includes aninitialization transistor comprising: a substrate; an active layerdisposed on the substrate; a first insulation layer on the active layer;a gate electrode disposed on the first insulation layer; a secondinsulation layer on the active layer; a drain electrode connected to adrain area of the active layer exposed by a contact hole of a secondinsulation layer, and a third insulation layer on the drain electrode,wherein a source area of the initialization transistor is connected tothe cathode electrode, wherein the cathode electrode applies aninitialization voltage to the initialization transistor, and wherein thecathode electrode penetrates the first insulation layer, the secondinsulation layer and the third insulation layer.
 11. The organic lightemitting display device of claim 10, wherein a first power voltage isapplied to the anode electrode, and a second power voltage is applied tothe cathode electrode, wherein the second power voltage is theinitialization voltage and is applied to the initialization transistor.12. The organic light emitting display device of claim 11, furthercomprising: a source electrode between the source area and the cathode.13. The organic light emitting display device of claim 10, wherein thepixel circuit further comprises a driving transistor, wherein a drainarea of the initialization transistor is connected to a gate electrodeof the driving transistor.
 14. The organic light emitting display deviceof claim 13, wherein a second power voltage is applied to the gateelectrode of the driving transistor as a gate signal.